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FERNS OF NORTH AMERICA.
side. They are attached to the rachis by a very short and slender
stalk. Their usual form is dimidiate-oblong; that is, tbey^i-ppeiF'
as if cut in two longitudinally, and the lower half removed, so
that the lower edge is entire, and straight, or often slightly hollowed
; the base, or edge nearest the rachis, is also straight and
entire; it is parallel with the rachis, or even overlaps it a little;
the upper edge is more or less lobed or incised, but in general
nearly parallel with the lower, and the end is rounded and slightly
lobcd. The point of attachment is, of course, at the angle between
the lower and basal edges. The terminal pinnule of each pinna,
and the basal one, which, indeed, very often proceeds from one
of the recurved branches ju s t below the origin of the pinna, are
broadly cuneate or transversely oblong in shape, the two sides
which meet at the point of attachment being equal; and the few
pinnules near the basal one arc shorter and more triangular than
the middle ones. The texture is delicately membranaceous, but
elastic; the color is a lively green, and both surfaces are very
smooth. The upper surface appears to be destitute of stomata;
and this may be the reason why water will not adhere to the pinnules,
but either falls off, or stands in spheroids ready to fall. The
veins are free: in the symmetrical basal and apical pinnules the
veinlets fork repeatedly from the very base; but in the oblong
middle pinnules there is a faint principal vein running close to the
lower edge ; and from this the veinlets diverge obliquely, and fork
about three times before reaching the superior margin. The incisions
of the superior margin are usually very narrow, and extend
only to about one-third of the breadth of the pinnule ; but in some
k m
FERNS OF NORTH AMERICA.
specimens from California and Oregon they are wider and considerably
deeper. The lobes are from four to six or seven in number
: in sterile fronds they arc minutely toothed at the end; but
in the commoner fertile fronds they are reflexed and changed in
character, so as to form somewhat crescent-shaped or transversely
elongated involucres of a pale-brownish color. The tips of the
veinlets extend into these involucres, and bear the sporangia on
the under or inner surface. In this peculiarity is the essential
generic character of Adianium. The spores of this species are
spheroid-tetrahedral, the three radiating angles marked with slen-
dervittre, or bands. They are mature in the latter part of summer ;
but the fronds remain until frost, often changing from green to
variegated shades of brown.
There do not seem to be any well-marked variations in this
fern. Ruprecht has a “ var. Alenticum',' the A d . boreale of Presl,
separated mainly on account of its smaller size and fewer parts.
The genus Adiantum contains eighty-thrcc species, according
to Mr. Baker’s estimate; but this number is reduced to sixty-
seven by the more recent and very careful recension of Keyser-
ling. The species vary in form from a simple and reniform frond
an inch or two in diameter to others with ample tripinnate and
even quadripinnate fronds. The species with distinctly bipartite
and radiated fronds are A d . patens, hispidulum, and flabelhda-
tum. A . patens is found in Mexico and Central America. It is
a smaller plant than A.pedatuni, and has deeply-sunken reniform
involucres. The other two occur in South-eastern Asia, the hispidulum
extending to Africa and to New Zealand, and the Jla-
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